Project Summary Trichomonas vaginalis is the causative agent of the most common, non-viral sexually-transmitted infection with >250 million new cases reported annually in the world and 5-7 million cases in the United States. More Americans are infected with this parasite than with any other eukaryotic pathogen. In addition to infections of the urogenital tract, trichomoniasis increases the risk of adverse pregnancy outcomes, HIV transmission, and cervical and prostate cancer. Only two drugs of the same class are FDA-approved for treatment, metronidazole and tinidazole. Although generally effective, treatment failures occur in a substantial fraction of patients (1- 17%), and the drugs have significant liabilities, with moderate to severe adverse effects when given by the only approved, oral route for trichomoniasis. Given its prevalence, its association with multiple disease outcomes, and an increase in drug-resistant strains, new antimicrobials against T. vaginalis are urgently needed. We discovered in preliminary studies that inhibitors of the proteasome, an essential cellular machinery for the degradation and recycling of cell proteins, effectively kill T. vaginalis and overcome metronidazole resistance. Based on these intriguing findings, the project has the overall objective to develop proteasome inhibitors as a novel therapeutic option for the treatment of trichomoniasis. We will perform whole-cell activity screens of several well-defined libraries of proteasome inhibitors to identify the most potent hits, confirm that the hits inactivate the targets in the parasite, and explore the in vivo efficacy of the best compounds in murine models of trichomonad infection. Together, the project is important and innovative in several key aspects, including the indication of trichomoniasis, the proteasome as a new drug target in the parasite, the use of whole-cell screening and well-defined, targeted chemical libraries, complementation of whole-cell screening with mechanistic biochemical studies, and a focus on topical drug administration as a novel therapeutic approach for the infection. The studies will be conducted by an outstanding multi-disciplinary research team with complementary expertise in parasitology, antimicrobial drug development, proteasome biology, and medicinal chemistry. This broad expertise will be instrumental for achieving the project objective to develop a new class of potent trichomonacidal agents.